This invention relates to a device for detecting inhomogeneities such as gas bubbles in a fluid in a conduit such as a liquid and, more particularly, to a device for detecting bubbles in liquid-filled pipes.
The detection of inhomogeneities such as bubbles within a fluid, for example a liquid, is of importance in monitoring and controlling a wide variety of processes. In high temperature processes using liquid coolants, for example, the presence of inhomogeneities in the form of bubbles can indicate regions of heat transfer deterioration. As another example, in refrigeration systems the presence of bubbles provides an indication of refrigerant insufficiency.
The usual technique for detecting bubbles within a pipe or conduit, however, is visual observation through a sight glass or other window. This technique requires a human observer and is not readily automated. Moreover, it cannot be used in much existing equipment, such as many automotive and home air conditioners which have no sight glasses or viewing windows.
In the instance of automotive and home air conditioners, the unavailability of sightless bubble detectors has contributed to a definite environmental problem. Upon suspicion of refrigerant insufficiency, it is common practice to empty all of the refrigerant gas, usually freon, into the atmosphere and to refill the system with the factory specified amount. The discharge of such gases into the atmosphere has a now well-recognized detrimental effect on the earth's protective ozone layer. See the Report of the Federal Task Force on Inadvertent Modification of the Stratosphere, Fluorocarbons and the Environment (U.S. Gov.'t., 1975).
While devices exist for automatically monitoring the bubble content of relatively large samples of open water, these devices are inappropriate for the non-obstructive monitoring of liquids contained in small diameter pipe or conduit. U.S. Pat. No. 3,046,780, for example, issued to the present inventor on July 31, 1962, discloses a fluid condition monitor comprising a towable acoustic resonator and a pair of coupled transducers. Impurities or disturbances in the fluid through which the device is towed are detected by variations in the quality factor, Q, of the resonating system. While it is suggested that this device can be used in pipelines, it would clearly be preferable to utilize a detection device which need not be placed within the pipe or conduit and thereby obstruct or impede fluid flow. Moreover, many pipes and conduits of interest have a sufficiently small diameter that impractically small resonators and impractically high frequency transducers would be required.